The present invention relates to a four-wheel drive system for vehicles which rotationally drives all four wheels of a vehicle by transmitting a rotational driving force from a driving source (engine or the like) to the front wheels and rear wheels, and more particularly relates to a four-wheel drive system for vehicles which is constructed so that the rotational driving force from the driving source is divided and transmitted to the front and rear wheels via a center differential mechanism.
Four-wheel drive vehicles in which both the front wheels and rear wheels are driven have been generally known in the past, and four-wheel drive vehicles in which a center differential mechanism is installed between the front wheels and rear wheels, and the vehicle is constructed so that the rotational driving force of the engine is divided and transmitted to the front and rear wheels via a center differential mechanism, are also known. In such four-wheel drive vehicles as well, axle differential mechanisms that are used to absorb the difference in rotation between the left and right wheels are installed on the front and rear wheels. Accordingly, in four-wheel drive vehicles of this type, a center differential mechanism and axle differential mechanisms for the front and rear wheels are required, so that a total of three differential mechanisms must be installed.
In cases where three differential mechanisms are thus separately installed, the power transmission system of the vehicle is increased in size, and the number of parts required is also increased, so that there is an increase in the cost of the vehicle. Accordingly, systems in which either the front or rear axle differential mechanism and the center differential mechanism are constructed as an integral unit have been proposed (for example) in Japanese Patent No. 2615086, Japanese Patent No. 3047016 and Japanese Patent No. 2621680. In the systems disclosed in these patents, the axle differential mechanism on the side of the front wheels and the center differential mechanism are constructed as an integral unit; accordingly, it is conceivable that the overall construction of the power transmission system could be reduced in size.
However, in the case of the system disclosed in Japanese Patent No. 2615086, the center differential mechanism is constructed with a pair of double planetary gears, and has a construction in which a bevel gear type axle differential mechanism is installed adjacent to this; accordingly, this system suffers from the problem of an extremely complicated and expensive construction. Furthermore, an integrated system is constructed by installing the bevel type axle differential mechanism inside a two-part casing that accommodates the center differential mechanism, and then connecting the two-part casing by means of bolts; as a result, the number of constituent parts required in the respective mechanisms is increased, and the number of places where shim adjustment is required is increased, so that the system is poor in terms of assembly characteristics. Moreover, a construction is used in which the system that is integrally constructed in this manner is supported by the transmission housing via a pair of left and right bearings so that rotation is possible; accordingly, the forces that act on the input gear members to the center differential mechanism and the output gears members to the rear wheel side must be supported by this pair of bearings, so that the bearing load is increased.
Furthermore, in the system disclosed in Japanese Patent No. 3047016, a hydraulic clutch that performs on-off operation of the center differential mechanism is installed, so that a portion of the system has a double-shift structure, thus resulting in a complicated overall structure. Moreover, the system disclosed in Japanese Patent No. 2621680 is constructed by installing two sets of planetary gear trains adjacent to each other; this system has a construction in which the rotational driving force from the engine is divided and transmitted to the left front wheel and the second planetary gear train by the first planetary gear train, and the rotational driving force that has thus been transmitted to the second planetary gear train is divided between the right front wheel and the rear wheels by the second planetary gear train. Accordingly, the gear ratios of these two sets of planetary gear trains with respect to the left and right front wheels must be set at the same value, so that the degree of freedom in design is low, and the setting of the gear ratios is difficult.
The present invention was devised in light of such problems. It is an object of the present invention to provide a simple and compact four-wheel drive system in which the center differential mechanism and either the front or rear axle differential mechanism are constructed as an integral unit.
In the present invention, in order to achieve such an object, a four-wheel drive system for vehicles is constructed with a center differential mechanism that divides and transmits a rotational driving force from a driving source (e.g., the engine E in the embodiment) to the front wheel side and rear wheel side, and an axle differential mechanism that divides and transmits the rotational driving force that has been divided by the abovementioned center differential mechanism to the left and right wheels on either the front wheel side or the rear wheel side. Furthermore, the center differential mechanism is constructed from a single pinion type first planetary gear device which has a first carrier member (e.g., the first carrier 13 in the embodiment) that is rotationally driven by the rotational driving force from the driving source, a first sun gear member (e.g., the first sun gear 11 in the embodiment) that is connected to the axle differential mechanism, and a first ring gear member (e.g., the first ring gear 14 in the embodiment) that is connected to the other of the two sides, i.e., either the front wheel side or rear wheel side, and the axle differential mechanism is constructed from a double pinion type second planetary gear device which has a second ring gear member (e.g., the second ring gear 24 in the embodiment) that is connected to the first sun gear member, a second sun gear member (e.g., the second sun gear 21 in the embodiment) that is connected to either the left or right wheel, and a second carrier member (e.g., the second carrier 23 in the embodiment) that is connected to the other of the two wheels, i.e., either the left or right wheel. These first and second planetary gear devices are installed adjacent to each other in a coaxial configuration.
In the four-wheel drive system constructed in this manner, the rotational driving force is divided and transmitted to the front wheel side and rear wheel side by the center differential mechanism, and the rotational force that has thus been divided is divided and transmitted to the left and right wheels by the [abovementioned] axle differential mechanism. Accordingly, the construction that divides and transmits the driving force is simple, and can easily be designed. Furthermore, since the single pinion type first planetary gear train that constitutes the center differential mechanism and the double pinion type second planetary gear train that constitutes the axle differential mechanism are disposed adjacent to each other in a coaxial configuration, the connecting structures of the respective elements can be simplified, and the overall construction can be made compact.
Furthermore, in another invention of the present application, a four-wheel drive system for vehicles is constructed with a center differential mechanism that divides and transmits a rotational driving force from a driving source (e.g., the engine E in the embodiment) to the front wheel side and the rear wheel side, and an axle differential mechanism that divides and transmits the rotational driving force divided by this center differential mechanism to the left and right wheels on either the front wheel side or rear wheel side. Furthermore, the center differential mechanism is constructed from a single pinion type first planetary gear device which has a first driven gear member (e.g., the output driven gear 3 in the embodiment) that is rotationally driven by the rotational driving force from the driving source, a first carrier member (e.g., the first carrier 13 in the embodiment) that is constructed as an integral unit with this driven gear member, a first sun gear member (e.g., the first sun gear 11 in the embodiment), a first ring gear member (e.g., the first ring gear 14 in the embodiment), and an output gear member (e.g., the rear wheel driving gear 15) that is formed as an integral part of the first ring gear member on the outer circumference of this first ring gear member, and that transmits the rotational driving force to the other of the two sides, i.e., the front wheel side or the rear wheel side, and the axle differential mechanism is constructed from a double pinion type second planetary gear device which has a second ring gear member (e.g., the second ring gear 24 in the embodiment) that is constructed as an integral unit with the first sun gear member, a second sung gear member (e.g., the second sun gear 21 in the embodiment) that is connected to either the abovementioned left wheel or the abovementioned right wheel, and a second carrier member (e.g., the second carrier 23 in the embodiment) that is connected to the other of the two wheels, i.e., either the left wheel or right wheel. Furthermore, a cylindrical retaining member is engaged and connected with the first carrier member that is constructed as an integral unit with the driven gear member, so that an input rotating member is constructed, and the second planetary gear device is disposed inside this input rotating member. Furthermore, the right end portion and left end portion of the input rotating member are supported rotatably by the housing via first and second bearings (e.g., the tapered roller bearings 61 and 62 in the embodiment). Moreover, an output rotating member which is constructed with an output gear member as an integral part on the outer circumference of the first ring gear member is supported rotatably at one end by the driven gear member via a third bearing (e.g., the ball bearing 64 in the embodiment), and is [likewise] supported rotatably at the other end by the housing via a fourth bearing (e.g., the ball bearing 63 in the embodiment).
In the four-wheel drive system constructed in this manner, the rotational driving force is divided and transmitted to the front wheel side and rear wheel side by the center differential mechanism, and the rotational driving force that has thus been divided is divided and transmitted t the left and right wheels by the axle differential mechanism. Accordingly, the construction that divides and transmits the driving force is simple, and can easily be designed. Furthermore, since the single pinion type first planetary gear train that constitutes the center differential mechanism and the double pinion type second planetary gear train that constitutes the axle differential mechanism are constructed with the respective elements connected as described above, the connecting structures can be simplified, and the overall construction can be made compact.
In the present invention, in particular, the second planetary gear device is disposed inside an input rotating member which is constructed by engaging and connecting a cylindrical retaining member with a first carrier member that is formed as an integral unit with the driven gear member, and this structure can be assembled by successively assembling the respective elements; furthermore, there is no need for bolts to connect the housing as in conventional systems, so that the assembled construction is simple.
Furthermore, the right end portion and left end portion of the input rotating member are supported rotatably by the housing via first and second bearings; accordingly, the force that acts on the driven gear member can be received by these first and second bearings. Meanwhile, the output rotating member which is constructed with an output gear member that is formed as an integral part of the first ring gear member on the outer circumference of the first ring gear member is supported rotatably at one end by the driven gear member via a third bearing, and is [likewise] supported rotatably at the other end by the housing via a fourth bearing; accordingly, the force that acts on the output gear member can be received by these third and fourth bearings, so that the forces that act on the driven gear member and output gear member can be dispersed and received by the first through fourth bearings, thus making it possible to lighten the load on these bearings.
Furthermore, in the present invention, a construction may be used in which the rotational driving force of the driving source is subjected to a speed change by the transmission, and is transmitted to the center differential mechanism via an output driving gear disposed on the output shaft of the transmission, and an output driven gear that engages with this output driving gear. In this case, the output driven gear is integrally connected to the first carrier member and disposed coaxially with this first carrier member, and a recess that opens to the side is formed on the internal diameter side of the gear body that has the output driven gear on its outer circumference. The first ring gear is supported by the output driven gear via a bearing member that is fitted and held in this recess, so that the first ring gear is free to rotate, and pinion accommodating spaces that can accommodate pinion gear members are formed in communication with the abovementioned recess in the output driven gear. Furthermore, shaft retaining holes that cut across these pinion accommodating spaces and extend in the axial direction through the left and right side walls that form the pinion accommodating spaces are formed in the output driven gear, and the first gear member is constructed by pinion shafts fitted in these shaft retaining holes.
Furthermore, the system is constructed so that outer-tooth pinion gears which are disposed on these pinion shafts so that these outer-tooth pinion gears are free to rotate, and which are positioned inside the pinion accommodating spaces, engage with the inner-tooth pinion gears of the first ring gear member.
In the planetary gear device constructed in this manner, the pinion gear members are supported so that these pinion gear members are free to rotate by pinion shafts inside the pinion accommodating spaces formed inside the output driven gear, so that the power transmission gear member that has the pinion accommodating spaces can function as a carrier member. Accordingly, there is no need to joint a carrier to the side surface of the output driven gear by welding or the like.
Furthermore, for example, the abovementioned output driven gear is manufactured by the lost-wax casting process from a material that has the high strength required in a gear part (chromium-molybdenum steel, chromium steel, carbon steel for machine structural use, nickel-chromium steel, nickel-chromium-molybdenum steel and the like).
As a result, an output driven gear which has the carrier constituent parts as integral parts can be constructed without welding, using a high-strength material of the type required in a gear member. Since welding is thus made unnecessary, there is no problem of the interference of welded parts with the pinion shafts or pinion gears, so that there is a high degree of freedom in the design of the carrier shape; furthermore, there is no need for an after-treatment process such as a welding strain removal treatment or the like. Moreover, since there is no need for a carrier assembly process or welding process, the number of assembly processes required can be reduced, and the number of constituent parts required is reduced so that the cost of parts can be reduced. Furthermore, since the carrier is also integrally formed from the high-strength material used for the output driven gear, the carrier constituent parts can be reduced in size, so that the construction of the planetary gear can be made more compact.
In particular, since the output driven gear requires a carbon impregnation treatment or the like, the carrier constituent parts that form an integral unit with this output driven gear are also simultaneously subjected to such a carbon impregnation treatment or the like, so that these parts have an extremely high strength. Furthermore, since these parts are manufactured by lost-wax casting, rounded parts (curved surface parts) can easily be formed in the connecting parts between the power transmission gear and the connecting arms that form the carrier; accordingly, the concentration of stress in these parts can be prevented, so that the carrier strength can be greatly increased.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.